1. Field of the Invention
The present invention relates to cyan and yellow ink compositions for ink jet recording, an ink set comprising the ink composition, and an ink jet recording method wherein a reaction solution and an ink composition are deposited onto a recording medium to conduct printing.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited onto a recording medium such as paper. This method has a feature that an image with high resolution and high quality can be realized at a high speed by means of a relatively inexpensive apparatus.
The ink composition used in the ink jet recording, in general, comprises water as a main solvent and, added thereto, a colorant and a wetting agent, such as glycerin, for preventing clogging. Regarding the colorant used in the ink composition for ink jet recording, a large number of water-soluble dyes have been used because of their high chroma, abundance, and good solubility in water and the like.
However, dyes are poor in various properties, such as lightfastness and waterfastness, and, hence, prints formed by using dye compositions have poor lightfastness and waterfastness. The waterfastness of the prints has been improved for a specialty paper, for ink jet recording, having an ink-absorptive layer, whereas it is unsatisfactory for plain papers.
On the other hand, pigments have better lightfastness and waterfastness than dyes. This has been led to studies on the use of pigments as colorants in an ink composition for ink jet recording. The pigments are generally insoluble in water. Thus, when the use of a pigment in an aqueous ink composition is contemplated, it is necessary to disperse the pigment in water with a resin and the like as "dispersant" before the preparation of an ink composition.
In order to stably disperse the pigment, the consideration should be given to the type and particle diameter of the pigment, the type of the resin used, dispersing means and the like. Many dispersing systems and inks for ink jet recording have hitherto been proposed in the art. For example, Japanese Patent Laid-Open No. 252467/1991 proposes an ink composition comprising water, a styrene/maleic acid copolymer, .epsilon.-caprolactum, and a pigment. Further, Japanese Patent Laid-Open No. 79680/1991 discloses an ink composition comprising an aqueous medium, a styrene/maleic acid copolymer, and a copper phthalocyanine pigment.
Studies on the use of pigments in inks for ink jet recording range from black inks to color inks.
The method in which a polyvalent metallic salt solution is applied on a recording medium followed by the application of an ink composition containing a dye having at least one carboxyl group has been recently proposed, for example, in Japanese Patent Laid-Open No. 202328/1993. The claimed advantage of this method is that the polyvalent metal ion combines with the dye to form an insoluble complex which can offer an image having waterfastness and high quality free from color bleeding.
Further, Japanese Patent Laid-Open No. 106735/1994 discloses the use of a color ink containing a surfactant or a solvent for imparting a penetrating property and a salt in combination with a black ink capable of being thickened or agglomerated with the salt. The claimed advantage of this method is that a high-quality color image having a high image density and free from color bleeding is realized. In this method, two liquids, i.e. a solution containing a salt as first and an ink composition as second, are printed in order to yield a good image.
Although pigments have better lightfastness and waterfastness, the type of usable pigments for this purpose is limited as compared with dyes. When pigments are actually used in the ink for ink jet recording, not only the lightfastness and the waterfastness but hue should be sufficiently studied. Properties such as lightfastness, waterfastness, and storage stability of ink compositions including a pigment for ink jet recording have been studied. However, studies on the hue of the ink composition including pigment and a change in hue of the ink composition when used in the ink jet recording method are made unsatisfactory.
We have now found that, in a color ink jet recording method, cyan and yellow ink compositions containing specific pigments can realize good images. Further, we have found that a combination of the above cyan ink composition or yellow ink composition with other color ink composition(s) can provide good images. Furthermore, we have found that these ink compositions, when used in an ink jet recording method using the so-called "two liquids" wherein a reaction solution and an ink composition are deposited to conduct printing, can yield good images.
Accordingly, an object of the present invention is to provide cyan and yellow ink compositions, for ink jet recording, which can realize good lightfastness and waterfastness and, in addition, good images, especially images having good hue.
Another object of the present invention is to provide an ink set, for ink jet recording, which can realize good lightfastness and waterfastness and, in addition, good images, especially images having good hue.
A further object of the present invention is to provide an ink jet recording method, using two liquids, which can realize good lightfastness and waterfastness and, in addition, good images, especially images having good hue.
According to one aspect of the present invention, there is provided a cyan ink composition comprising at least one pigment represented by the following formula (I): ##STR1## wherein x is an integer of 0 to 3; or, a pigment represented by the following formula (II): ##STR2## or a mixture of the pigment represented by the formula (I) with the pigment represented by the formula (II).
According to another aspect of the present invention, there is provided a yellow ink composition for ink jet recording, comprising a pigment represented by the following formula (III): ##STR3## wherein Y.sub.1 to Y.sub.8 each independently represent a chlorine or hydrogen atom and R represents o-phenylene or 2,6-xylyl, or C.I. Pigment Yellow 74, 138, 150 or 180.
According to still another aspect of the present invention, there is provided an ink set for ink jet recording, comprising a cyan ink composition, a magenta ink composition, and a yellow ink composition, wherein the cyan ink composition is the above cyan ink composition of the present invention.
According to a further aspect of the present invention, there is provided an ink set for ink jet recording, comprising a cyan ink composition, a magenta ink composition, and a yellow ink composition, wherein the yellow ink composition is the above yellow ink composition of the present invention.
According to a still further aspect of the present invention, there is provided an ink set for ink jet recording, comprising a cyan ink composition, a magenta ink composition, and a yellow ink composition, wherein the cyan ink composition is the above cyan ink composition of the present invention and the yellow ink composition is the above yellow ink composition of the present invention.
According to another aspect of the present invention, there is provided a ink jet recording method, comprising the step of: depositing a reaction solution containing a reactant and an ink composition onto a recording medium,
wherein the ink composition is the above cyan ink composition of the present invention or an ink composition in the above ink set, and PA1 the reactant breaks the state of dispersion and/or dissolution of the pigment to cause agglomeration.